Method and system for controlling an avatar using computer vision

ABSTRACT

A method and system for controlling an avatar using computer vision is presented. A video stream representing a background and a foreground is received. A user in the foreground is segmented from the background and classified to produce effector information. An avatar may be controlled based on the effector information.

BACKGROUND

[0001] 1. Field

[0002] This invention relates to computer animation and computer vision.Specifically, this invention relates to a method and system forcontrolling an avatar.

[0003] 2. General Background and Related Art

[0004] A two- or three-dimensional (3D) computer-animated character suchas an avatar may be controlled in a number of ways. For example, in thecomputer game industry, a character may be controlled via an inputdevice such as a control pad. In a graphical interface, an avatar may becontrolled via a mouse or a combination of a mouse and a keyboard.Although limited training may be sufficient to teach users how tooperate such control devices, translating various actions performed onsuch control devices to corresponding animated acts is often neitherintuitive nor natural.

[0005] Attempts have been made to achieve animated character controlbased on human gestures. A human user may make certain gestures thatcorrespond to certain control signals. Such gestures may be detected andinterpreted via automatic means. For example, video frames of a humanuser making different gestures may be captured and analyzed so thatrelevant gestures can be identified and understood. The interpretationof the detected gestures is then used to control the movement of ananimated character such as an avatar.

[0006] To detect a user's gestures, it is often necessary to firstdetect where the user is located and when the user makes gestures.Distinctive marks may be used to effectuate detection of the user.Examples of such marks include special clothing, clothing with coloredartifacts, or special devices such as infrared tags. As such, the usermust wear or carry marks that are obtainable and distinguishable fromthe user's surroundings. Automated processing identifies thesedistinctive marks from the images, notes location and movement of themarks, and infers what gestures occurred. Since these approaches requirea user to wear marks, the user may feel inconvenienced or uncomfortable.

[0007] Another approach requires users to make gestures at predefinedpositions. While this approach does not require the user to wear orcarry marks, it forces the user to memorize the correspondence betweendifferent positions and control effects.

[0008] Therefore, what is needed is a method and system to control anavatar in a more natural and direct manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 illustrates an avatar controller system according to thepresent invention.

[0010]FIG. 2 is a system-level block diagram according to an embodimentof the present invention.

[0011]FIG. 3 is a system-level block diagram according to an embodimentof the present invention.

[0012]FIG. 4 is a flow diagram of a method according to an embodiment ofthe present invention.

[0013]FIG. 5 is a flow diagram of a method according to an embodiment ofthe present invention.

DETAILED DESCRIPTION

[0014] The following detailed description refers to the accompanyingdrawings that illustrate exemplary embodiments of the presentinventions. Other embodiments are possible and modifications may be madeto the embodiments without departing from the spirit and scope of theinvention. Therefore, the following detailed description is not meant tolimit the invention. Rather, the scope of the invention is defined bythe appended claims.

[0015] It will be apparent to one of ordinary skill in the art that theembodiments as described below may be implemented in many differentembodiments of software, firmware, and hardware in the entitiesillustrated in the figures. The actual software code or specializedcontrol hardware used to implement the present invention is not limitingof the present invention. Thus, the operation and behavior of theembodiments will be described without specific reference to the actualsoftware code or specialized hardware components. The absence of suchspecific references is feasible because it is clearly understood thatartisans of ordinary skill would be able to design software and controlhardware to implement the embodiments of the present invention based onthe description herein with only a reasonable effort and without undueexperimentation.

[0016] Moreover, the processes associated with the presented embodimentsmay be stored in any storage device, such as, for example, a computersystem (non-volatile) memory, an optical disk, magnetic tape, ormagnetic disk. Furthermore, the processes may be programmed when thecomputer system is manufactured or via a computer-readable medium at alater date. Such a medium may include any of the forms listed above withrespect to storage devices and may further include, for example, acarrier wave modulated, or otherwise manipulated, to convey instructionsthat can be read, demodulated/decoded and executed by a computer.

[0017] A method and system for controlling an avatar using computervision, as described herein, involves receiving a video streamrepresenting a background and a foreground. A user in the foreground issegmented from the background and classified to produce effectorinformation. An avatar is controlled based on the effector information.

[0018]FIG. 1 illustrates an avatar controller system according to thepresent invention. As shown, system 100 comprises video camera 130,computer vision technology system 140, and monitor 160. Person 120stands in front of background 110. Video camera 130 captures an image ofperson 120 against background 110, and transmits the image to computervision technology system 140.

[0019] Computer vision technology system 140 processes a video streamreceived from video camera 130, and produces information necessary torender an avatar 150 on monitor 160. When person 120 moves her hands orhead in order to make various gestures, the movements of person 120control avatar 150 on monitor 160. Accordingly, if latency effects areignored, avatar 150 may move in lock-step fashion with person 120. Forinstance, if person 120 raises her hand to wave at video camera 130,avatar 150 may raise its hand as well. In other embodiments, avatar 150may be partially controlled by an input device (not shown), such as amouse, keyboard, or a combination thereof.

[0020] System 100 may classify users to enable various kinds of users tocontrol avatar 150. Thus, person 120 in system 100 may be replaced byanother user, such as, for example, a robot or a bear. In system 100,avatar 150 may represent any kind of artificially created character. Forinstance, avatar 150 may be rendered as a skeletal figure comprisingbones and joints, or as a fully-clothed human or a cartoon character.The present invention may have applicability in many applications, suchas gaming software, simulation software, toys, and software for personsundergoing physical therapy.

[0021]FIG. 2 is a system-level block diagram of system 200 according tothe present invention. System 200 comprises video segmentor 230,classifier 220, and controller 240. Video segmentor 230 receives a videostream 210 that may represent a background, such background 110 in FIG.1, and a foreground. Video segmentor 230 segments a user in theforeground, such as person 120, from the background. Classifier 220classifies the user. Accordingly, effector information is produced. Theeffector information may be inputted into controller 240. The effectorinformation may be expressed in any number of coordinates, such as intwo- or three-dimensional coordinates. Controller 240 controls an avatarbased on the effector information. As such, controller 240 outputs imagedata 250 for use by, for example, a display (not shown).

[0022]FIG. 3 is a system-level block diagram according to anotherembodiment of the present invention. System 300 comprises video camera310, video segmentor 340, controller 380, and display 315. It is to benoted that various components of system 300 may be implemented asseparate interconnected modules or as one or more multifunctionaldevices.

[0023] Video camera 310 may be a computer capture camera, such as a CCDor CMOS camera. In an exemplary embodiment, video camera 310 may beaimed at a background. Video camera 310 may be calibrated with respectto the background such that a background reference image is produced.Specifically, video camera 310 may memorize the background so that videocamera 310 may extract a user's image from the background. Video camera310 may capture a video stream which may include a user in front of thebackground. The video stream need not be stored by video camera 310.Calibration may be performed without a need for a person to place his orher hands in a special position relative to video camera 310;calibration may occur when a person is not standing in front of thebackground.

[0024] Video segmentor 340 may comprise background/foreground classifier350 and hand and head tracker 360. Video segmentor 340 receives a datastream which includes a background and a foreground. Video segmentor 340may segment a user in the foreground, including the hands and head ofthe user, from the background, and classify the user to produce effectorinformation. Video segmentation methods are well known in the art andmay be incorporated into the present invention. For instance, televisionbroadcasts of weather forecasters, the Intel Play Me2Cam Virtual GameSystem by Intel Corporation, and Logitech's GameCam employ such methods.

[0025] Specifically, background/foreground classifier 350 may separatethe user from the background in the video stream and classify the user.Background/foreground classifier 350 may separate the user from thebackground in various ways, such as by subtracting the backgroundreference image from each frame of the video stream.Background/foreground classifier 350 may also analyze successive videoframes to determine which objects, or portions thereof, are moving andwhich are stationary. In still other implementations, the background maycomprise a blue screen, and a user may be distinguished by filteringsuch a fixed background from each video frame.

[0026] Hand and head tracker 360 may track the hands and head of theuser to produce two-dimensional image coordinates of the hands and head.Hand and head tracker 360 may employ an alpha channel and intelligentguessing algorithms. An alpha channel may include foreground andbackground information of a segmented image. Points may be plotted atvarious locations in a segmented image, such as at points within theforeground that lie along axes intersecting various edges of theforeground. If sufficient plots are made, hand and head tracker 360 maydetermine the likely locations of the hands and head of the user.Accordingly, finding of the hands and head of the user may occurirrespective of color. Further, a person or other user in front of videocamera 310 need not wear special clothing, carry special trackingobjects, or make movements in a predetermined position.

[0027] Controller 380 receives effector information outputted by videosegmentor 340. Controller 380 may comprise coordinate converter 370,inverse kinematics engine 390, and graphics rendering engine 395.Coordinate converter 370 may convert the two-dimensional imagecoordinates of the hands and head to three-dimensional imagecoordinates. Such conversion may not be necessary if a two-dimensionalavatar is to be rendered. Various coordinate conversion techniques maybe employed by coordinate converter 370, such as those using a constantcoordinate value. A coordinate value of varying depth may also beemployed, wherein distance between the user and video camera 310 isestimated, and coordinate values are assigned accordingly.

[0028] Inverse kinematics engine 390 may receive effector information inthe form of 2D or 3D coordinates. To control an avatar, inversekinematics engine 390 may map such coordinates to produce acorresponding movement of the avatar. Inverse kinematics may beperformed for each of the effected joints and bones of an avatar. IntelCorporation produces the Intel 3D Toolkit, which includes an inversekinematics engine that may be especially appropriate for implementationin the present invention.

[0029] In an exemplary implementation, movement of a 3D avatar may beeffected by corresponding movements of users. For example, head, leftarm, and right arm movement of a user may act as effector information.To cause a 3D avatar to mimic a user facing the 3D avatar, the 3Dcoordinates of the left hand of the user may control right arm movementof the avatar. Similarly, 3D coordinates of the right hand of the usermay control left arm movement of the 3D avatar.

[0030] In system 300 in FIG. 3, rendering engine 395 in controller 380may render the avatar on display 315 based on information provided byinverse kinematics engine 390. Rendering engine 395 may be programmedusing the OpenGL or Direct3D application programmatic interfaces (APIs),and may comprise graphics hardware. Display 315 may be chosen based ongraphics hardware in 3D rendering engine 395.

[0031]FIG. 4 is a flow diagram of method 400 according to an embodimentof the present invention. In block B410, a video camera is calibratedwith respect to a background. In block B420, a video stream thatincludes a user in a foreground is captured. Then, in block B440, theuser is segmented from the background and classified so as to produceeffector information. An avatar is controlled based on the effectorinformation, as shown in block B450.

[0032]FIG. 5 illustrates blocks B440 and B450 of FIG. 4 in greaterdetail. Dashed box 501 of FIG. 5 corresponds to dashed box 401 of FIG.4. In block B510, after the video stream is captured, a user isseparated from the background and classified. In block B520, the headand hands of the user are tracked. In block B530, coordinate conversionis performed. In block B550, inverse kinematics are performed on theeffector information. The avatar is rendered on a display in block B560.

[0033] The foregoing description of the preferred embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. Various modifications to these embodiments arepossible, and the generic principles presented herein may be applied toother embodiments as well. For instance, other parts of a user, such asarms, legs, and feet, may function as effectors to control an avatar. Assuch, hand and head tracker 360 in FIG. 3 may be modified.

[0034] Moreover, the invention may be implemented in part or in whole asa hard-wired circuit, as a circuit configuration fabricated into anapplication-specific integrated circuit, or as a firmware program loadedinto non-volatile storage or a software program loaded from or into adata storage medium as machine-readable code, such code beinginstructions executable by an array of logic elements such as amicroprocessor or other digital signal processing unit.

[0035] As such, the present invention is not intended to be limited tothe embodiments shown above but rather is to be accorded the widestscope consistent with the principles and novel features disclosed in anyfashion herein.

What is claimed:
 1. A method for controlling an avatar using computervision, said method comprising: receiving a video stream representing abackground and a foreground; segmenting a user in said foreground fromsaid background and classifying said user to produce effectorinformation; and controlling an avatar based on said effectorinformation.
 2. The method according to claim 1, wherein said foregroundincludes a moving user.
 3. The method according to claim 2, wherein saideffector information includes three-dimensional coordinates of the headposition of said moving user.
 4. The method according to claim 3,wherein said segmenting said user includes segmenting the head of saidmoving user.
 5. The method according to claim 2, wherein said effectorinformation includes three-dimensional coordinates of the hand positionsof said moving user.
 6. The method according to claim 5, wherein saidsegmenting said user includes segmenting the hands of said moving user.7. The method according to claim 1, further comprising: calibrating avideo camera with respect to said background to produce a backgroundreference image; and capturing said video stream.
 8. The methodaccording to claim 7, wherein said segmenting said user comprises:separating, in said video stream, said user from said background; andtracking the head and the hands of said user to produce two-dimensionalimage coordinates of said head and said hands.
 9. The method accordingto claim 8, wherein said separating said user from said backgroundincludes subtracting said background reference image from each frame ofsaid video stream.
 10. The method according to claim 8, wherein saidcontrolling further comprises: receiving said effector information;performing inverse kinematics based on said effector information toproduce a movement of said avatar; and rendering said movement of saidavatar on a display screeen.
 11. The method according to claim 10,further comprising converting said two-dimensional image coordinates tothree-dimensional coordinates before said performing.
 12. The methodaccording to claim 11, wherein said converting includes converting saidtwo-dimensional image coordinates to said three-dimensional coordinatesusing a constant depth coordinate value.
 13. The method according toclaim 10, wherein said effector information includes at least one ofcoordinates of the left hand of said user, coordinates of the right handof said user, and coordinates of the head of said user.
 14. The methodaccording to claim 13, wherein said movement of said avatar includes atleast one of head movement, left arm movement, and right arm movement.15. The method according to claim 14, wherein said controlling furthercomprises: controlling said right arm movement of said avatar using saidcoordinates of the left hand of said user; and controlling said left armmovement of said avatar using said coordinates of the right hand of saiduser.
 16. The method according to claim 10, wherein bones of said avatarare effected, and wherein said performing includes performing kinematicsfor each of the effected bones of said avatar.
 17. The method accordingto claim 10, wherein joints of said avatar are effected, and whereinsaid performing includes performing kinematics for each of the effectedjoints of said avatar.
 18. A system for controlling an avatar usingcomputer vision, said system comprising: a video segmentor configured toreceive a video stream representing a background and a foreground, andto segment a user in said foreground from said background and classifysaid user to produce effector information; and a controller configuredto control an avatar based on said effector information.
 19. The systemaccording to claim 18, further comprising a video camera calibrated withrespect to said background to produce a background reference image,wherein said video stream is captured using said video camera.
 20. Thesystem according to claim 19, wherein said segmentor separates, in saidvideo stream, said user from said background, and tracks the head andhands of said user to produce two-dimensional image coordinates of saidhead and said hands.
 21. The system according to claim 20, wherein saidsegmentor subtracts said background reference image from each frame ofsaid video stream.
 22. The system according to claim 20, wherein saidcontroller is further configured to receive said effector information,perform inverse kinematics based on said effector information to producea movement of said avatar, and render said movement of said avatar on adisplay screeen.
 23. The system according to claim 22, wherein saidcontroller is further configured to convert said two-dimensional imagecoordinates to three-dimensional coordinates.
 24. The system accordingto claim 23, wherein said effector information includes at least one ofthree-dimensional coordinates of the left hand of said user,three-dimensional coordinates of the right hand of said user, andthree-dimensional coordinates of the head of said user.
 25. Acomputer-readable medium encoded with a plurality ofprocessor-executable instructions for: receiving a video streamrepresenting a background and a foreground; segmenting a user in saidforeground from said background and classifying said user to produceeffector information; and controlling an avatar based on said effectorinformation.
 26. The computer-readable medium of claim 25, furthercomprising processor-executable instructions for: calibrating a videocamera with respect to said background to produce a background referenceimage; and capturing said video stream.
 27. The computer-readable mediumof claim 26, wherein said segmenting said user comprises: separating, insaid video stream, said user from said background; and tracking the headand the hands of said user to produce two-dimensional image coordinatesof said head and said hands.
 28. The computer-readable medium accordingto claim 27, wherein said separating said user from said backgroundincludes subtracting said background reference image from each frame ofsaid video stream.